This invention relates to a process for bonding parts made of unsaturated polyester resins. The bonding is carried out at room temperature without previous surface treatment.
When bonding molded parts of unsaturated polyester resins, in particular SMC and BMC, it is customary to carry out a preliminary treatment on the surface of the parts to be joined before they are bonded together. The purpose of this treatment is to roughen or activate the surface; in addition, it removes or renders inactive any external or internal mold release agent present on the surface. Suitable processes for this purpose have been described in numerous publications (see e.g. U.S. Pat. Nos. 3,647,513, 3,703,426, 3,838,093, 3,962,498, 4,004,050, 4,397,707, 3,714,127, 3,886,122, 3,933,051, 3,812,003, 4,247,676, 4,,336,298, 4,373,082, 4,390,678, 4,444,976, 4,552,934, 4,595,445 and 4,624,996).
Some publications describe adhesives and adhesive processes which enable polyester resin parts to be bonded without a preliminary surface treatment: a) "Fusor 320/321 and Fusor 320/322", Product Information, Lord Corp., Erie, Pa. (USA), Jun. 10, 1985; b) Anil B. Goerl, "New Pliogrip Hybrid Structural Adhesive", Effective adhesive Applications for the Automotive Eng., Soc. of Manufact. Eng., Oct. 21-23, 1986, The Westin Hotel, Detroit, Mich., USA; c) EP 0 328 808, d) U.S. Pat. No. 4,923,756, e) U.S. Pat. No. 4,876,308. All these publications, however, describe bonding processes in which setting of the adhesive takes place at elevated temperatures, preferably above 100.degree. C.
It is an object of the present invention to provide a quick setting adhesive which ensures good substrate adherence on SMC and similar materials at low temperatures, preferably in the region of room temperature, without a preliminary surface treatment.
Setting under ambient temperature conditions has economical advantages, as it dispenses with the need for heating devices and the attendant consumption of energy. Moreover, heat curing in many cases cannot be carried out because of construction or manufacturing (technical) limitations, or because of distortions or surface defects ("read-through") due to differences in the coefficients of thermal expansion.
Priming has the economical disadvantage in that it entails an additional process step which is difficult to automate. Moreover, the substances used for priming are in many cases not harmless, from an industrial hygiene point of view, under the conditions of application normally employed in practice.